Spinal fixation system

ABSTRACT

A clamp assembly for securing a bone anchor to a generally cylindrical rod. The clamp assembly includes a first portion, a second portion and a compressible ball carried by the second portion, the ball having a through hole for receiving the generally cylindrical rod. The first portion includes first and second flanges, each of the first and second flanges defining an aperture for receiving a portion of the bone anchor. The first and second flanges are movable from a first position in which the first and second flanges are separated by a gap to a second position in which the first and second flanges are drawn toward each other. The first and second flanges include first and second opposing surfaces, respectively, the first and second opposing surfaces being angled relative to one another in the first position.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/341,658 filed on Jan. 14, 2003. The disclosure of the aboveapplication is incorporated herein by reference.

INTRODUCTION

The spinal column is a highly complex structure which houses andprotects critical elements of the nervous system. In spite of thesecomplexities, the spinal column is a highly flexible structure, capableof a high degree of curvature and twist through a wide range motion.Genetic or developmental irregularities, trauma, chronic stress, tumors,and disease, however, can result in spinal pathologies which eitherlimit this range of motion, or threaten the critical elements of thenervous system housed within the spinal column.

A variety of systems has been disclosed in the art which achieveimmobilization of portions of the spinal column by implanting artificialassemblies in or on the spinal column. These assemblies may be generallyclassified as anterior, posterior or lateral implants. Posteriorimplants are attached to the back of the spinal column generally bycoupling to the pedicles with screws, or through hooks that attach underthe lamina. In either case, the implants generally include elongatesupport rod elements which are coupled to the screws or hooks toimmobilize two or more sequential vertebrae, for example to hold themstable so that adjacent bones may be fused with bone graft.

During implantation of a spinal fixation system of the type having anelongated support rod and anchors, it is important to provideadjustability between the support rod and the anchors. Adjustabilityfacilitates ideal placement of the bone anchors relative to the spine.Preferably, the adjustability between the support rod and the anchorsallows the supports rods to translate relative to the anchors and alsoallows for pivotal movement of the anchors relative to the support rod.The spinal system must also be able to arrest relative movement betweenthe support rod and the anchors after implantation so that the spinalsegments are post-operatively immobilized.

While known spinal fixation systems have proven to be useful for variousapplications, they are all associated with drawbacks. In this regard,the fixation screws or hooks of most known systems are difficult orimpossible to adequately tighten to arrest relative movement between theanchors and support rod after implantation. Overcoming this limitationtypically involves a complex clamping arrangement or an arrangement thatrequires undue tightening. Use of known systems is often a tediousprocess, which is inconsistent in result and adds unwanted time to aprocedure.

Accordingly, it remains a need in the art to provide an improved spinalsystem clamping mechanism for coupling a rod and a bone anchor thatovercomes the above discussed and other drawbacks of the prior art.

SUMMARY

The present teachings provide a clamp assembly for securing a boneanchor to a generally cylindrical rod. In one aspect, the clamp assemblyincludes a first portion, a second portion and a compressible ballcarried by the second portion, the ball having a through hole forreceiving the generally cylindrical rod. The first portion includesfirst and second flanges, each of the first and second flanges definingan aperture for receiving a portion of the bone anchor. The first andsecond flanges are movable from a first position in which the first andsecond flanges are separated by a gap to a second position in which thefirst and second flanges are drawn toward each other. The first andsecond flanges include first and second opposing surfaces, respectively,the first and second opposing surfaces being angled relative to oneanother in the first position.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 is a perspective view of a spinal fixation system constructed inaccordance with the teachings of a preferred embodiment of the presentinvention, the spinal fixation system shown arranged in an exemplaryconstruct and operatively attached to a human spinal column;

FIG. 2 is a perspective view of one of the spinal anchors and anassociated clamp assembly of FIG. 1 removed from the construct of FIG. 1for purposes of illustration;

FIG. 3 is a partially exploded side view of a portion of the constructof FIG. 1;

FIG. 4 is a perspective view of the clamp assembly of FIG. 2;

FIG. 5A is a side view of the clamp assembly of FIG. 4 shown with thefirst and second flanges normally spaced apart;

FIG. 5B is a view similar to FIG. 5A illustrating the first and secondflanges drawn together; and

FIG. 6 is a cross-sectional view taken along the line 6-6 of FIG. 5A.

DESCRIPTION

The following description of the preferred embodiments of the presentinvention is merely exemplary in nature and is in no way intended tolimit the subject invention or its application or uses.

With general reference to the drawings, a spinal fixation systemconstructed in accordance with the teachings of the preferred embodimentof the present invention is illustrated and generally identified atreference character 10. As shown in the environmental view of FIG. 1,components of the system 10 have been arranged in an exemplary constructfor attachment to a portion of a spinal column 12 of a human patient.The components of the system 10 of the present invention used in theconstruct of FIG. 10 generally include a linkage in the form of agenerally cylindrical support rod 14, a plurality of spinal anchors 16for engaging the spinal column 12, and a plurality of clamp assemblies18 securing the spinal anchors 16 to the cylindrical rod 14.

The spinal anchors are illustrated throughout the drawings as bonescrews 16. Alteratively, it will be understood by those skilled in theart that other types of anchors known in the art may be employed fordirectly engaging the spine. For example, the anchors may alternativelybe hooks that attach under the lamina of the spine.

With particular reference to FIGS. 2 and 3, one of the spinal anchors 16and an associated one of the clamp assemblies 18 are illustrated infurther detail. The spinal anchor 16 includes an upper threaded shaftportion 20 and a lower threaded shaft portion 22. The upper threadedshaft portion 20 threadably engages a nut 24 when the spinal anchor 16is secured to a linkage or rod 14 in a manner discussed below. The rodis preferably a generally cylindrical rod 14.

The clamp assemblies 18 each adjustably interconnect one of the spinalanchors 16 that engage the spinal column 12 with the rod 14. In theexemplary construct of FIG. 1, the system 10 of the present invention isillustrated to include three clamp assemblies 18A, 18B, 18C. A first ofthe clamp assemblies 18A is shown in further detail in FIGS. 2-6 and isillustrated to generally include a body 26 having a first portion 28 forengaging the rod 14 and a second portion 30 for engaging the spinalanchor 16. The body 26 of the clamp assembly 18A is shown to generallyhave a C-shape with an intermediate portion or arm that defines anopening 32 for receiving the rod 14. In the embodiment illustrated, theopening 32 is partially spherical and is adapted to adjustably receive acompressible locking member or ball 34.

The compressible locking ball 34 is shown particularly in FIGS. 5A and5B and the cross-sectional views of FIG. 6. As shown, the locking ball34 is generally spherical in shape and includes an aperture or throughhole 36 which passes therethrough for receiving the rod 14. As willbecome more apparent below, the clamp body 26 and the ball 34 cooperateto form a ball and socket joint that allows pivotal movement of the rod14 relative to the anchor 16. This pivotal movement is about animaginary center of the ball 34. The locking ball 34 is normallypermitted to universally move within the opening 32. A slit 38 isprovided in the locking ball 34 to facilitate compression of the balland resulting clamping on the rod 14.

The through hole 36 is defined by a generally cylindrical inner surface.The generally cylindrical inner surface preferably includes at least onerelieved channel 50. In the embodiment illustrated, the cylindricalinner surface is shown to include five relieved channels 50. Theparticular number of relieved channels 50 will be understood to be amatter of design choice and may vary from that shown in the drawings.The relieved channels 50 allow for a more uniform collapse of thelocking ball 34. In this manner, the locking strength of the clampassembly 18 is increased independent of the position of the ball 34within the partially spherical opening defined by the clamp 34.

As perhaps most particularly shown in the cross-section view of FIG. 6,at least a portion of the through hole 36 tapers from a first end 52 ofthe through hole 36 to a second end 54 of the through hole 36 toward acenter of the locking ball 34. As shown, the through hole 36 preferablytapers from the first end 52 towards the center and also from the secondend 54 towards the center. A center portion 56 of the through hole 36has a constant diameter. This configuration of the through hole 36allows the locking ball 34 to be loaded and not impinge on a contouredrod.

In the embodiment illustrated, the through hole 36 passes through thecenter of the locking ball 34. Alternatively, the through hole 36 may beeccentric to the sphere defined by the locking ball 34. By orienting thethrough hole 36 eccentric to the sphere, adjustments can be made byrotating the locking ball 34 within the clamp body 26.

The clamp body 26 further includes a first or upper flange 40 and asecond or lower flange 42. In the embodiment illustrated, the upper andlower flanges 40 and 42 are symmetrical about a plane extendingtherebetween. The upper and lower flanges 40 and 42 are shown to begenerally circular in shape. The intermediate portion or arm of theclamp body 26 that extends between the flanges 40 and 42 is disposedradially relative to the upper and lower flanges 40 and 42. The upperand lower flanges 40 and 42 define distinct but aligning apertures 44and 46 (see FIG. 4), respectively. The apertures 44 and 46 are bothassociated with recesses 48 to receive either a nut 24 or a partiallyspherical shaped portion 60 of the screw 16, respectively. In thismanner, it is impossible to put the clamp assembly 18 on the rod 14upside down.

As shown particularly in FIG. 5A, the first and second flanges 40 and 42are normally spaced apart by a gap. The first and second flanges 40 and42 include first and second opposing surfaces 62 and 64, respectively.As shown in FIG. 5A, when the first and second flanges 40 and 42 arenormally spaced apart, the opposing surfaces 60 and 64 are angledrelative to one another.

Upon tightening of the nut 24, movement of the clamp body 26 relative tothe rod 14 is arrested. Explaining further, tightening of the nut 24serves to draw the upper and lower flanges 40 and 42 together causingthe intermediate portion of the clamp body 26 to compress squeeze thelocking ball 34 and correspondingly clamp the rod 14. Relative movementis also arrested between the locking ball 34 and the clamp body 26.

Importantly, the clamp body 26 is formed to include sufficient spacingbetween the upper and lower flanges 40 and 42 so that the gap 60 isalways maintained throughout the range of tightening. In this manner,clamping forces are more efficiently transferred to the locking ball 34.The clamp body 26 is illustrated in a fully clamped condition in FIG.5B. As shown, the opposing surfaces 62 and 64 are oriented generallyparallel to one another.

With particular reference to FIGS. 1, the clamp assemblies 18B and 18Cwill be understood to be identical. The clamp assemblies 18B and 18Cdiffer from the clamp assembly 18A in that the second portion 30 istangentially oriented relative to the first and second flanges 40 and42. In other words, the intermediate portion or arm that connects thefirst and second flanges 40 and 42 is offset to one side from a radialposition. This offset allows the rod 14 to be positioned closer to theanchor 16 and reduces the medial lateral profile of the construct.Otherwise, it will be understood that the clamp assemblies 18A-18C areidentical.

The foregoing discussion discloses and describes merely exemplaryarrangements of the present invention. One skilled in the art willreadily recognize from such discussion, and from the accompanyingdrawings and claims, that various changes, modifications and variationscan be made therein without departing from the spirit and scope of theinvention as defined in the following claims.

1. A clamp assembly for securing a bone anchor to a generallycylindrical rod, the clamp assembly comprising: a first portionincluding first and second spaced apart flanges, the first and secondspaced apart flanges both defining apertures for receiving a portion ofthe bone anchor, wherein the first and second flanges include first andsecond opposing surfaces, respectively, the first and second opposingsurfaces being angled relative to one another before the first andsecond flanges are drawn toward one another; a second portion; and acompressible ball carried by the second portion, the ball having athrough hole for receiving the generally cylindrical rod.
 2. The clampassembly of claim 1, wherein the through hole defined by a generallycylindrical inner surface has at least one relieved channel.
 3. Theclamp assembly of claim 1 in combination with the bone anchor, the boneanchor having an upper threaded portion extendable through the aperturesof the first and second flanges and engaging a nut such that tighteningof nut draws the first and second flanges toward one another and thesecond portion compresses the ball.
 4. The clamp assembly of claim 3,wherein the first and second opposing surfaces are generally parallel toone another when the nut is tightened.
 5. The clamp assembly of claim 4,wherein the second portion circumferentially surrounds the ballsubstantially completely when the first and second flanges are drawntogether.
 6. The clamp assembly of claim 1, wherein the generallycylindrical surface includes a plurality of relieved channels.
 7. Theclamp assembly of claim 6, wherein the plurality of relieved channelsextend generally parallel to an elongated axis of the rod.
 8. The clampassembly of claim 1, wherein the compressible ball and the secondportion of the clamp assembly define a ball and socket joint such thatthe rod is permitted to pivot relative to the clamp assembly about acenter of the ball.
 9. A clamp assembly for securing a bone anchor to agenerally cylindrical rod, the clamp assembly comprising: a firstportion including first and second flanges, each of the first and secondflanges defining an aperture for receiving a portion of the bone anchor,the first and second flanges movable from a first position in which thefirst and second flanges are separated by a gap to a second position inwhich the first and second flanges are drawn toward each other, thefirst and second flanges including first and second opposing surfaces,respectively, the first and second opposing surfaces being angledrelative to one another in the first position; a second portion; and acompressible ball carried by the second portion, the ball having athrough hole for receiving the generally cylindrical rod.
 10. The clampassembly of claim 9, in which the first and second opposing surfaces aregenerally parallel to one another in the second position.
 11. The clampassembly of claim 10, wherein the second portion circumferentiallysurrounds the ball substantially completely when the first and secondflanges are in the second position.